Electrical conductor



Dec. 7, 1943. G. R. BROWN ELECTRIC CONDUCTOR Filed June 18, 1940 POLYMER/G INSULA TION ll/E WH/ OPPER PA PER PULP WEA THERPROOF/ NG ATTORNEY Patented Dec. 7, 1943 ELECTRICAL CONDUCTOR George B. Brown,Newark, N. 1., assignoi' to Western Electric Company, Incorporated, NewYork, N. Y., a corporation of New York Application June 18, 1940, SerialNo. 341,098

8Claims.

This invention relates to electrical conductors, and more particularlyto insulated electrical conductors which are particularly adapted foruse where the conductor proper is to be soldered for electricalconnection. I

In telephone apparatus, radio apparatus and other electrical apparatus,insulated wire is used in large quantities for interconnecting theelectrical devices and units of which such apparatus are-composed. Inmany instances such connector wires are preferably permanently connectedto wire may be tinned, coated with an enamel-like material such as thatcommercially known as nylon, or polyethylene ester, or that commerciallyknown as Vistanex,. which is at the same time a satisfactory insulatingmaterial and also does not hinder the penetration of molten soldertherethrough and may even act as a soldering flux to assist in making agood soldered connection. A wire thus coated may then be provided with'asheath over the coating, but not'adherent thereto, of seamlesslyinter-felted paper pulp fibers, and this sheath may be externally coatedwith a suitable weatherproofln material, e. 8. cellulose acetate, vinylacetate, nylon, polyester, or the like.

, Other objects and features of the invention will appear from thefollowing detailed description of an embodiment thereof in an insulatedelectrical conductor constructed in accordance with the invention, takenin connection with the accompanying drawing in which the single figurerepresents a portion of such a conductor and its various coverings. v

In carrying out the invention as herein disclosed, a metal wire H ofsuitably conductive material, e. g. copper, is coated with tin as at 12,by dipping into a bath of molten tin or electrolytically or in any othersuitable manner. Upon thi tin coating is then formed a sheath or layerl3, which is so far as possible free-from solutions of continuity of anykind, such as cracks, p n holes and the like, and which is tough,smooth, impervious and satisfactorily electrically insulating. Thematerial of the sheath l3 should not soften or become tacky attemperature about 100 C. or a little higher for reasons which willappear hereinafter. Also, for reasons to be set forth later, thismaterial must be such as will not interfere with or hinder thesatisfactory access of molten solder to the tin coating and'successfulsoldering thereto, but should preferably act as a flux when in contactwith molten solder.

Over the layer i3 is formed a seamless sheath ll of interfelted fibersof cellulose material, e. g. paper pulp. A suitable method and apparatusto effect this are disclosed in U. S. Patent No.

2,180,554, granted November 21, 1939, tov John N.

electrical value of the insulating complex on the metallic core. Asuitable apparatus and method for forming the external coating ii on thefiber sheath ll are disclosed in detail in U. S. Patent No. 2,217,337,granted October 8, 1940 to Waldemar C. Ewaldson et al., to whichreference may be had for details of the same.

In the forming of the sheath H over the layer it, the formed sheath ofwet, felted pulp is dried by passing the wet sheathed core through aheated oven so that substantially all the moisture is driven out of thefelted pulp, leaying a seamless sheath of material much like a. softporous blotting paper, devoid of moisture. It is found in practise thatthe temperature at the inner surface of this sheath during this dryingoperation rises to values of the order of to C., but not appreciablyover 100 C. Since it is usually desired that the pulp sheath It be notadherent to the layer IS on which it rests, the material for the layerI3 is preferably selected to be such as will not soften appreciably orbecom tacky or sticky at temperatures of the order of 100 C.

The at present preferred material for the layer it is one of thesubstances or mixtures of substances, chemically superpolymers ofpolyamids, which are commercially known as nylon. This material, ascommercially available, is prepared to have melting points within alarge range of values for different purposes and uses. That preferredfor the present invention may have a values may be preferred for specialuses.

Another material which may be satisfactorily employed insome cases forthe layer l3, may be selected from the general class of superpolymers oforganic polyesters, of which typical members are polymerizedpolyethylene sebacate and polyethylene succinata-ioi' example. Thisclass of materials also exists with members and mixtures oi! membersshowing a wide range of melting points, from which materials having thedesired melting or softening points and other suitable characteristicsmay be selected.

A third class of materials from'which members and mixtures of members sutable for layer l3 may be selected'is that of the polymerized oleflnes.For example, there is commercially available at the present time amaterial commerically known as Vistanex, a highly polynie'rizedisobutylene. Highly polymerized ethylenes, amylenes and isoamylenes arealso to be found having suitable physical characteristics.

Common characteristics of these materials which are of peculiar interestin the present invention are of three principal kinds. First, the layerl3 made from these materials has a high electrical insulating value andresistance to breakdown under electrical stress. Second, and notably inthe case of nylon, the layer i3 is mechanically tough, flexible andelastic over a wide temperature range, and may be bent, coiled andkinked with the wire core, and even materially stretched with the wire,without developing any cracks, tears or other solutions of continuity todamage its insulating value. Third, these materials have the curiousproperty that they can be soldered through without material hindrance tothe soldering operation or damage to the soldered joint. It evenappears, especially in the cases of nylon and Vistanex that thesematerials act in somedegree as soldering fluxes and soassist in theproduction of a sound soldered joint,

The mode of application used to form the layer l3 will depend to someextent at least upon the particular material selected in any given case,but requires no novel apparatus or method other than those usuallyemployed in enamelling or coating strands with molten materials or withsolutions or dispersions of them in a suitable volatile vehicle.However, a-preferred mode of application or" the layer over the core isby extruding the softened or molten material thereon without employingany vehicle.

In the preferred form of the invention, an important feature is that thelayer l3 be wholly formed and set to a point where the sheath it can bedeposited and wholly dried on it without any adhesion being effectedbetween the layer and the sheath. Furthermore, it may be important thatthe method used to form the outer film or weatherproof coating l5 besuch that substantially none of thevehicle used in this procedure shallpenetrate the sheath Hi and reach thesurface of the layer 13 to causeany softening-ortackiness of this layer with consequent adhesion. of thesheath thereto.

When the completed insulated conductor is constructed in the mannerdescribed, it is found to have an insulation of unusually highelectrical strength and endurance. Furthermore, when such a wire is tobe permanently connected toa metal member, the sheath l4 and coating l5are easily removed from the end or other portion at which connection isto be made, since these adhere firmly together but are not adherenttothe layer !3 underneath. The layer l3 need not be removed, and indeedshould not be, before the soldering is undertaken, for the material ofthis layer melts and vaporizes without charrlng or leaving any residue,when in contact with molten solder, and even seems to act as a solderingflux, so that firm and sound soldered joints are made without the use ofany flux in addition to the material of the layer l 3.

As noted, in the preferred form of the invention, the sheath I 4 is madeto be non-adherent to, though closely embracing, the layer I3 in orderthat the sheath l4 and coating 15 may be easily stripped when necessary.However, there are procedures wherein the insulated conductor of theinvention has .distinct advantages even though there is adhesion of thesheath M to the layer l3. Thus in some cases, where a sheathed conductoris to be soldered or brazed to some metal members, it may be quicker andeasier, as a manufacturing procedure, to burn off the sheath from theportions to be connected. In such a case, the peculiar property of thisparticular type of organic material of disintegratingand vaporizingwithout leaving any char or other solid res due, is of distinctimportance and value. Thus in its broadest phase the invention turns onthe unusually high insulation properties of the composite insulation,together with its endurance of electrical stress and of mechanicalstress, as well as its resistance to atmospheric moisture, which appearto' be due to the combination of the layer l3 of this particular type ofmaterial, the sheath M of. felted paper pulp fibers, and theouterweatherproof film or coating l5 adherent to but not interpenetrant intothe substance of the fibrous sheath. 7 In a narrower phase, the value ofthe invention derives from the residueless disintegration of the layerl3 when sufliciently heated, so that the compoundsheath of insulationmay be burned ofi as desired without interfering with subsequentsoldering on the portion of the core thus made bare. Finally, and in thenarrowest phase, the

principal usefulness lies in the case where the sheath I4 isnonradherent to the layer l3, and the layer i3 need not be removed,after the sheath l4 and coating I5 are stripped, before soldering.

In the preceding are disclosed three specific kinds of materialsuitable, within the purview of the invention, for the layer i3, namely,the polyamide complexes commrrclally known as nylon, the analogoushighly complex polyesters of the type of polymerized polyethylenesebacate, and the related highly polymerized olefines, such as theisobutylene polymers commercially known as Vistanex and the highlypolymerized ethylene 'or amyl'ene products. Each of these presentsindividual members with melting points, sharp or vague, having a widerange, from materials which are soft at room temperatures to some thatdisintegrate at high temperatures without melting. Not all of these, andyet a large number and variety, are useful in applicant's invention. Foruse in the appended claims, applicant therefore selects the phrasenormally solid and non-charring Tpolymeric insulating material andsimilar phrases to represent that portion or the class of suchsubstances which has the properties of being electrical insulators, ofbeing a tough solid at ordinary temperatures, and of disintegrating attemperatures of the order of that of melted solder without leaving achar or other solid residue.

The particular embodiments herein disclosed are illustrative and may bevariously modified and departed from without departing from the spiritand scope of the invention as pointed out in and limited only by theappended claims.

What is claimed is:

1. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon consisting of a layer of normally solid and non-charringsuperpolymeric insulating material selected from the class consisting ofsuperpolyamids, superpolyesters and superpolyolefines directly on thestrand, a seamless com bustible sheath of felted' paper pulp fibers overthe layer, and a coating of weatherproofing material on the gross outersurface of the sheath.

2. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon consisting of a layer of normally solid and non-charringsuperpolyamidic insulating material directly on the strand, a seamlesscombustible sheath of felted paper pulp fibers over the layer, and acoating of weatherprooflng material on the gross outer surface of thesheath.

3. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon consisting of a layer of normally solid and non-charringsuperpolyesteric insulating material directly on the strand, a seamlesscombustible sheath of felted paper pulp fibers over the layer, and acoating of weatherproofing material on the gross outer surface of thesheath.

4. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingthe manufacture of communications apparatus means thereon consisting ofa layer of normally solid and non-charring superpolyolefinic insulatingmaterial directly on the strand, a. seamless combustible sheath offelted paper pulp fibers over the layer, and a coating ofweatherproofi'ng material on the gross outer surface of the sheath.

5. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon including a layer of normally solid and non-charringsuperpolymeric insulating material selected from the class consisting ofsuperpolyarnids, superpolyesters and superpolyolefines directly on thestrand, and a seamless combustible sheathof felted paper pulp fibersover the layer. s

6. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon including a layer of normally solid and non-charringsuperpolyamidic insulating material directly on the strand, and'aseamless combustible sheath of felted paper pulp fibers over the layer.

7. An insulated electrical conductor for use in the manufacture ofcommunications apparatus comprising a conductive strand and insulatingmeans thereon including a layer of normally solid and non-charringsuperpolyesteric insulating material directly on the strand, and aseamless combustible sheath of felted paper pulp fibers over the layer.

8. An insulated electrical conductor for use in comprising a conductivestrand and insulating means thereon including a layer of normally solidand non-charring superpolyolefinic insulating material directly on thestrand, and a seam.- less combustible sheath of felted paper pulp fibersover the layer.

GEORGE R. BROWN.

